We know of no good way to rule ((227)) out, while still ruling ((228)) in.
Dayal (1996) suggests that `full' NPs such as which person and
whose mother are R-expressions while who and whose
are pronouns. R-expressions, unlike pronouns, are subject to Condition C.
((226)) is, then, ruled out as a violation of Condition C since the person and which person are co-indexed and the person
c-commands which person. If we accept Dayal's argument, we
have a principled reason for allowing overgeneration of relative clauses
that violate the internal head constraint, the reason being that
the XTAG grammar does generate binding theory violations.